Lighting Ckt

I would suggest the use of 3 separate CBs. Each CB must be an RCD. If the lighting is exterior, you may have to reconsider the use or the setting of the RCD.

Can you post a sketch of the lighting circuit? It makes it much easier to understand what's going on, and advise accordingly.

we are not in that stage still, we have just a design basis and from which working sketch. for your reference here i am giving the full design basis- if it could help to explain the complexity-

"Lighting circuits shall be four wire (3L+N) and will be supplied from three-pole CB with 300 mA max trip rating earth lickage protection."

thanks

This looks like an extract from either a Regulation or a requirement from your end-user. In either case, you can't do much except go along with it.

This arrangement does have the advantage that if you have a fault on one line, everything is disconnected, and you know it's safe to get in and fiddle about to isolate the fault, without the risk of inadvertently touching something that's still live.

yea you are right, that mean i have to use L1, L2 and L3 for that particular CB in same location only, if i used all those 3 ph at three different location then all area will be block out due to of one are fault..

If you can guarantee that the 3 circuits are well separated after the CB's, you could get around it by using three 3-pole CB's (thus meeting the requirement), but only connecting from L1 on one, L2 on the next & L3 on the third. Cost difference between 1-pole & 3-pole CB's probably insignificant.

Either that, or install loads of emergency lighting, or hand out torches!

It's not uncommon in the US to use 277 VAC lighting on 4-wire circuits with 1-pole or 3-pole CB's. 277 VAC is derived from line-to-neutral on 480 VAC line-to-line transformer secondaries, and in a 480 VAC, 3-phase lighting panel, it is quite common.

If the lighting panel is a 120/208V and the lights are on a 2 pole 208Voltage, you will need to keep the 3 pole breaker.

the light panel is feed from 230 V 50 Hz supply, can i do the distribution like this for example. 5L1------2x42W Luminer 8 No's at room no 1

5L2------2x42W luminer 10 No's at room no 2

and 5L3------2x42W luminer 8 No's at room no 3

if so, due to of fault at room no 1, all the three room will be blocked out.

please comment.

If you've got a single-phase supply, it sounds like someone has cited the wrong Regulation. I suggest you query it with whoever wrote the specification.

yea, thanks john, you are right, just i have a conversation with that engineer, actually he intendant to luminary voltage rating and not supply. again he insist that in US the lighting done by 4 wire system but my doubt is unclear still.

Sorry, this is about as far as I can go. I'm out of my field, here; I just know a few basics about supply wiring.

If the engineer you spoke with is responsible for specifying the system, I suggest you do your design, and pass it up the line with a note that "it is a consequence of the System Specification that a failure on any one of the lighting circuits will result in disconnection of all three". That should at least keep your job safe!

Good luck, John

Something else has just occurred to me - in post #9 you said:

"the light panel is feed from 230 V 50 Hz supply",

but then in post #11

"... he insist that in US the lighting done by 4 wire system "

It's very unlikely to be either 230V or 50Hz in the US. Where is this system going to be installed?

yea, john, the thing is like this, the design consultant is from US and system is going to be executed at Qatar with American standard.

now thing is quite clear and i will go by what Andy suggested and convey same to the consultant.

thanks to all

almost all lighting is done on 277v in the US from circuits which originate from a 480 v 3ph 4 wire source. the correct way to wire these lights is to feed each individual room/set of lights from a single pole 277v breaker and either run them through a light switch, buy switch duty breakers , or run them through a lighting contactor. a lighting contactor allows you to cut down on conduit runs by using your 120v panel to power your light switches it also lets you turn off individual sets of lights (by breaker) and still light the rest in the case of a large area. i have an area of a factory which has 24 fixtures fed by 4 breakers through a lighting contactor so customer can light portions of the building or all as he wishes. Same thing can be done for 240v except that you need 2 pole breakers (and of course a 240 v panel to feed from)

Putting 3 rooms on a 3-pole breaker is not common at all (I've looked at a lot of breaker panels and don't recall ever seeing such a situation), and I wouldn't do it. Typically, room lighting is done with separate 1-pole breakers.

One poster said to use a 3-pole breaker on a 2-phase circuit in the case of 120/208 volts. I wouldn't do that either. Two pole breakers are used for that.

It would be better if either 3 x 1 pole or just one pole of each 3 pole (if that is what you have), as in the case of 1 x 3 pole CB, then ALL the lighting will go off when a failure occurs on one phase only.....even a single bulb (incandescent) can short when it reaches the end of its life, throwing everything into darkness!!

With 3 separate CBs, only the circuit with the problem goes off!!! Much better and MUCH easier to fault find too as you a) know which circuit has the fault immediately and b) it could be that you might have some light from the other circuits to work by......!!

Quid Pro Quo!

I believe there is some language in the new NEC that says if curcuits share a common neutral they must have a common trip breaker. If the circuits are completely independant with each circuits neutral going all the way back to the neutral bar, then individual breakers may be used. This then, gets into conduit fill as it can add several load carrying wires to a conduit requireing de-rating the wire or requiring more conduits. -- JHF

if you want the breaker to trip for line to neutral faults then you may use a slash rated cb, i.e. a 300mA ,3 pole, 208/120 v ,.

if i use slash rated CB, is there still requirement of ELCB as slash rated CB can work both L-L and L-G fault condition.